Molecular DFT structure and packing effect of thiodipropionic and dithiodiglycolic acids and salts

Molecular and periodic DFT structure calculations of thiodipropionic and dithiodiglycolic acids, Sn[(CH2)(COOR)]2 (n = 1,2, R = H, Na), were performed. Computed structures were analyzed and compared to the experimental data (a Cs conformation is favored in solution than C2 in solid state). Four close and low-energy optimized conformations were analyzed: C2v, C2, Cs and C1. Small changes in the conformation stability (ΔG) and symmetry group were observed in polar medium. Periodic DFT-GGA approaches have been performed to determine the importance of weak interaction upon the crystal structure of the thiodipropionic acid, e.g., S-H and/or O-H hydrogen bonding. More SH and OH dispersed bands were observed in the optimized structure. Using a full analysis of the DOS of O-H or S-H bonding contributions, a notable interlayer bonding in the parent structure was revealed. Therefore, the presence of such weak interaction O⋯Na+ or O⋯H may thus change the point group symmetry of the crystal upon packing effect.